1. Field of the Invention
This invention relates to a method for making foamed articles and, more particularly, to a method for making foamed styrene polymer articles suitable for use as precision level frames, the articles being characterized by a high degree of dimensional stability, a cellular core and a substantially non-cellular, integral peripheral smooth surfaced shell.
2. The Prior Art
The manufacture of level instruments generally requires relatively highly skilled labor in the final production phases to precisely align the level and plumb vials thereof in relation to the working surfaces of the level frame. In U.S. Pat. No. 3,311,990, there is disclosed a level frame fabricated with precision notched mounting means for engaging and retaining the vial. In assembling the level, the assembler inserts the vial into the mounting means and secures cover plates on each side of the frame over the vial. The cover plates serve to automatically align the longitudinal axis of the vial in a plane normal to the working surfaces of the frame, thereby obviating the time consuming process of having the assembler visually observe, judge and adjust the position of the vial to obtain a predetermined bubble alignment. Thus, it is critical to the utility of such level frames that the dimensions of the notches and the distance that they are spaced apart be maintained within relatively close tolerances.
The material generally used for the manufacture of level frames is extruded aluminum. One of the problems encountered with aluminum levels is that because of the excellent heat conductivity of aluminum, it is very uncomfortable for workmen to use such levels for outdoor projects on cold winter days.
Although the substitution of non-conductive thermoplastic resins for aluminum in the level frames would appear to be an easy solution to the problem, the manufacture of levels and, particularly levels of the type disclosed in U.S. Pat. No. 3,311,990 is not easily accomplished because of the difficulty in molding frames having mounting means meeting the precision tolerances discussed above.